the continuing need to increase fuel efficiency and reduce emissions and noise in commercial transport aircraft has driven the increasing use of high bypass ratio turbo-fan engines. As appreciated by those skilled in the art, as the bypass ratio of the engine increases, so does their overall diameter. For under-wing mounted power plants, the large fan diameter necessitates either increasing the landing gear length to provide the necessary ground clearance, this option being undesirable due to the resulting increased weight and integration of problems of the longer landing gear, or to mount the engine closer to the wing.
Traditional under-wing engine mounting methodologies involve mounting the engine pylon to the lower surface of the wing. However, as the overall diameter of the turbo-fan engines has increased this methodology is approaching its limit in terms of the vertical separation provided between the engine and the lower surface of the wing, such that further fan diameter increases are becoming increasingly difficult to accommodate without compromising the overall aircraft configuration in terms of either the landing gear length or wing dihedral.